scholarly journals Method for the synthesis of broadband devices with an optimal characteristic of the power conversion factor, matching the time-varying load impedance.

2021 ◽  
Author(s):  
P.V. Boykachev ◽  
◽  
I.A. Dubovik ◽  
V.O. Isaev ◽  
◽  
...  
Keyword(s):  
Experimental Studies ◽  
Operating Conditions ◽  
Coefficient Function ◽  
Engineering Systems ◽  
Load Impedance ◽  
Radio Line ◽  
Wide Range ◽  
Complex Criterion ◽  
Broadband Matching ◽  
Optimal Characteristic

A method is proposed for the synthesis of broadband matching devices that adapt radio engineering systems to the changing load impedance in a wide range of natural conditions of their operation. The results of experimental studies of the effect of operating conditions on the impedance of VHF and UHF radio antennas with matching devices are presented. An invariant of the sensitivity of the reflection coefficient function to changes in the load impedance is obtained, on the basis of which a complex criterion for the synthesis of broadband matching devices is developed. A broadband matching circuit was synthesized for the AD-44/CW-TA-30-512 antenna device, which provides a gain in the potentially achievable radio line range of up to 5% in relation to the standard matching device. An analytical mathematical model of a broadband matching device is developed and based on it, a matching device adaptive to the changing impedance of the AD-25/CW-3512 antenna is synthesized, providing an average gain in the potentially achievable range of the radio line from 2% to 15% in the framework of the presented experimental studies.

scholarly journals Method for synthesis of matching devices for broadband radio engineering systems with unstable load impedance based on the method of real frequencies

Doklady BGUIR ◽  
2021 ◽  
Vol 19 (5) ◽  
pp. 70-78
Author(s):  
I. A. Dubovik ◽  
P. V. Boykachev
Keyword(s):  
Power Transmission ◽  
Operating Conditions ◽  
Transmission Factor ◽  
Coefficient Function ◽  
Engineering Systems ◽  
Load Impedance ◽  
Radio Engineering ◽  
Broadband Radio ◽  
Complex Criterion ◽  
Combination Of Methods

The aim of this work is to develop a method for the synthesis of matching devices for broadband radio engineering systems with varying impedance in different operating conditions. To achieve this goal, a criterion (complex criterion) is proposed for minimizing the value of the modulus of the sensitivity invariant of the reflection coefficient function to a change in the load impedance with restrictions on the square of the deviation of the power transmission ratio from a given level. It is proposed to use a combination of methods of real frequencies together with the shown complex criterion, which made it possible to implement an effective approach to the synthesis of matching devices for broadband radio engineering systems with an unstable load impedance. To verify the approach, a matching device was synthesized, which made it possible to reduce the loss of the power transmission factor level transmitted to the UHF/VHF antenna of the AD-44 / CW-TA-30-512 range when it is located in various operating conditions by at least 50 % in relation to losses obtained with a standard matching device.

A New Analytical Model of a Centrifugal Compressor and Validation by Experiments

2010 ◽  
Vol 26 (1) ◽  
pp. 37-45 ◽  
Author(s):  
H. Pourfarzaneh ◽  
A. Hajilouy-Benisi ◽  
M. Farshchi
Keyword(s):  
Conceptual Design ◽  
Centrifugal Compressor ◽  
Experimental Studies ◽  
Design Tool ◽  
Operating Conditions ◽  
Experimental Results ◽  
Design Phase ◽  
Robust Model ◽  
Conceptual Design Phase ◽  
Wide Range

AbstractIn the conceptual design phase of a turbocharger, where emphasis is mainly on parametric studies, before manufacturing and tests, a generalized and robust model that implies over a wide range properly, is unavoidable. The critical inputs such as compressor maps are not available during the conceptual design phase. Hence, generalized compressor models use alternate methods that work without any supplementary tests and can operate on wide range. One of the common and applicable modeling methods in design process is the ‘Dimensionless Modeling’ using the constant coefficient scaling (CCS). This method almost can predict the compressor characteristics at design point. However, at off design conditions, error goes up as mass flow and speed parameters increase. Therefore, the results are not reliable at these points. In this paper, a variable coefficient scaling (VCS) method is described. Then, a centrifugal compressor is modeled using the VCS method. To evaluate the model and compare it with the experimental results, some supplementary experiments are performed. Experimental studies are carried out on the compressor of a S2B model of the Schwitzer turbocharger in the turbocharger Lab., at Sharif University of Technology. The comparison between the experimental results and those obtained by the VCS method indicates a good agreement. It also suggests that the present model can be used as an effective design tool for all operating conditions.

scholarly journals Program for determination of zones of gold concentration on sluices of washing devices

2021 ◽  
Vol 895 (1) ◽  
pp. 012002
Author(s):  
V S Alekseev ◽  
R S Seryi
Keyword(s):  
High Performance ◽  
Two Phase Flow ◽  
Experimental Studies ◽  
Operating Conditions ◽  
Phase Flow ◽  
Technological Parameters ◽  
Two Phase ◽  
Alluvial Gold ◽  
Wide Range ◽  
Host Rocks

Abstract Currently sluice washing devices are the most common in alluvial gold mining. Their use provides a sufficiently high performance, relatively low power consumption, and acceptable recovery of valuable components. The theoretical provisions of traditional hydraulics make it possible to determine all the main parameters of the movement of particles of rocks and gold in the pulp, however, in real operating conditions of the sluice box, their actual values will differ greatly from the calculated ones, especially if there are solid fractions in the pulp with a particle size of more than 20 mm. This is explained by significant fluctuations in the values of the surface, average and bottom velocities of the two-phase flow, vertical pulsation velocity in conditions of constrained movement of the different fractional composition of rocks. The article presents the results of experimental studies to identify the dependence of the distance traveled by an individual gold particle and host rocks in a two-phase flow through a sluice, the bottom of which is lined with trapping coatings, on the design and technological parameters of the flushing device. The mathematical model for determining this distance formed the basis of the Gold Enriching program. The program allows, in a wide range of initial data, to determine the zones of concentration of gold of a certain size at the sluice boxes.

Elastohydrodynamic Film Thickness in Concentrated Contacts: Part 2: Correlation of Experimental Results with Elastohydrodynamic Theory

1986 ◽  
Vol 200 (3) ◽  
pp. 219-226 ◽  
Author(s):  
R J Chittenden ◽  
D Dowson ◽  
C M Taylor
Keyword(s):  
Film Thickness ◽  
Experimental Studies ◽  
Elastohydrodynamic Lubrication ◽  
Operating Conditions ◽  
Experimental Results ◽  
Experimental Techniques ◽  
Dimensionless Parameters ◽  
Wide Range ◽  
Theoretical Predictions ◽  
Computational Procedures

The existence of a coherent film of lubricant between highly loaded machine elements has been recognized for many years. Over this period of time measurements of film thickness have gone hand in hand with theoretical analyses in the field now known as elastohydrodynamic lubrication. The experimental techniques of capacitance, electrical resistance and X-ray measurement have been supplemented by the use of optical interferometry while the analytical expressions obtained with the use of elegant simplifications have been superseded by those developed from extensive and comprehensive computational procedures. These developments in experimental techniques have yielded a substantial number of measurements of both minimum and central film thickness. Likewise, the advent of the digital computer has allowed the derivation of a large number of solutions to the problem of elastohydrodynamic lubrication of concentrated contacts. All these results, covering a wide range of geometrical conditions, are to be found in the literature, yet little attempt appears to have been made to assemble a representative set of experimental data to permit a detailed evaluation of the theoretical formulae for elliptical contacts. The second part of this paper therefore considers the correlation between a number of experimental studies covering a wide range of operating conditions and geometries, and the predictions of recent elastohydrodynamic theory. Some of the important aspects of each set of experimental results are then considered and examples are provided which illustrate the following points: 1. Good estimates of lubricant film thickness may be obtained from the theoretical expressions recently derived, even when the dimensionless parameters involved are outside the ranges considered in the derivation of the formulae. 2. The discrepancies which exist between theoretical predictions and some of the measured film thicknesses are nevertheless quite large, even when the dimensionless parameters are within their usual limits. On the whole there is good agreement between experiment and theory, while the general trend of the results indicates that theoretical predictions may underestimate the minimum film thickness by about 10 per cent and the central film thickness by about 25 per cent. This measure of agreement is quite remarkable when the extreme difficulty of interpreting the magnitudes of effective and very thin mean film thicknesses between machined components in various forms of experimental equipment is considered.

scholarly journals ANALYSIS OF THE CONDITIONS OF OCCURRENCE AND SUPPRESSION OF LATERAL VIBRATIONS IN MICROWAVE POWER FETS

2020 ◽  
Vol 258 (3) ◽  
pp. 4-21
Author(s):  
V. L. Aronov ◽  
E. M. Savchenko ◽  
D. M. Moseykin ◽  
A. D. Pershin ◽  
D. G. Drozdov
Keyword(s):  
Experimental Studies ◽  
Element Model ◽  
Excitation Power ◽  
Point Of View ◽  
Operating Conditions ◽  
Stability Factor ◽  
Lateral Instability ◽  
Wide Range ◽  
Amplifier Stage ◽  
The Stability

Lateral instability is inherent in power transistors structures, consisting of several simple transistors connected in parallel. The large number of transistor elements complicates the analysis of such instability. The introduction of suppressing resistors makes it possible to prevent the occurrence of lateral oscillations, however there are no unambiguous criteria for achieving stability this way. The matter is further complicated by the fact that transistor exhibits nonlinear operation in a typical amplifier stage, and the operating conditions in many cases correspond to a relatively wide range of frequencies. In this paper, we present an analysis of lateral instability of a power amplifier stage, created on a basis of modern GaN field-effect transistor (FET). We had designed all dies and circuits for this FET. The main feature of the analysis is that we carried it out in the time domain, which made possible to estimate the stability of the stage not only under the excitation power pulse, but also after the end of the pulse. Our approach makes it possible to assess the stability of the amplifier between the excitation pulses, which is very important from the operational point of view. We calculated the estimates of operational stability and stability factor using a simplified transistor model, with the multi-element model reduced to a two-element model. Nevertheless, the results of the estimates retain their significance in real conditions, when the introduction of suppressing resistors creates a significant margin of stability, including the actual operating frequency band of the stage. To date, the data we have obtained after the manufacture of the samples only partially confirms the calculated estimates, due to the complexity of managing the experimental studies. However, there are no recorded results, which deny our estimates for the model.

Experimental Nusselt Number in Rod Bundles Cooled by Heavy-Liquid Metals

2018 ◽  
Author(s):  
J. Pacio ◽  
M. Daubner ◽  
T. Wetzel ◽  
I. Di Piazza ◽  
M. Tarantino ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Nusselt Number ◽  
Complex Geometry ◽  
Liquid Metals ◽  
Experimental Studies ◽  
Operating Conditions ◽  
Heavy Liquid ◽  
Large Temperature ◽  
Wide Range ◽  
Fuel Assemblies

A detailed safety assessment of innovative Generation IV reactor designs with heavy-liquid metal coolants, such as lead and lead-bismuth eutectic (LBE), requires an evaluation of the maximum core temperature in several postulated scenarios. Considering the complex geometry of fuel assemblies (FAs), and the low Prandtl number of the coolants, this flow scenario is challenging for the models used in numerical simulations, e.g. for relating the turbulent transport of momentum and heat. Thus, reliable experimental data are needed for validation. In recent years, a series of comprehensive heat transfer tests in fuel pin bundle simulators was performed at ENEA (Italy) and KIT (Germany) in the framework of the European collaborative projects THINS and SEARCH. Both grid and wire spacer geometries are considered, in a wide range of operating conditions (temperature, flow velocity and power density) representative of the ALFRED and MYRRHA fuel assemblies, in natural and forced-convective flow regimes. Although different experimental approaches were followed by each group (e.g. thermocouple position and average data treatment), there is a relatively good agreement on results in the overlapping regions. These experimental studies indicate that the mean Nusselt number is in well agreement with the predictions of empirical correlations developed for sodium systems. In particular, for wire-spaced FA, heat transfer results show values close to the Kazimi-Carelli correlation both for low and high flow rates at ENEA and KIT respectively. For grid-spaced FA, results are more in agreement with Ushakov correlation. Furthermore, large temperature differences are measured by thermo-couples installed at selected rods and sub-channels. A discussion on the influences of the spacer design and bundle size is included. This wide comparison allows an overview of the research on the HLM cooled fuel assembly in Europe.

Modeling and Experimental Investigation of Bubble Formation in Shear-Thinning Liquids

2017 ◽  
Vol 139 (7) ◽  
Author(s):  
Mohamad Taghi Esfidani ◽  
Mohammad Reza Oshaghi ◽  
Hossein Afshin ◽  
Bahar Firoozabadi
Keyword(s):  
Power Law ◽  
High Speed ◽  
Gas Flow ◽  
Bubble Formation ◽  
Experimental Studies ◽  
Methyl Cellulose ◽  
Operating Conditions ◽  
Wide Range ◽  
Bubble Sizes ◽  
Newtonian Liquids

This investigation presents both theoretical and experimental studies on the size of a growing bubble in power-law non-Newtonian liquids. At first, some previous works on the prediction of bubble size in Newtonian liquids have been extended by considering the balance of forces acting on the bubble at the moment of separation. Predicted bubble sizes were validated against the experimental results for a wide range of operating conditions, including different gas flow rates and needle diameters as well as a wide range of physical properties of the Newtonian liquids. Furthermore, in order to determine the size of the bubbles formed in power-law non-Newtonian liquids with a similar analysis, the effective shear rate of bubble growth was calculated in which the rheological properties of fluid were taken into account and subsequently the viscosity of the fluid was modified. Theoretically obtained bubble sizes for non-Newtonian liquids are in a good agreement with our experimental high-speed video observations of three carboxyl methyl cellulose (CMC) solutions.

Chemical Kinetic Models for Enhancing Gas Turbine Flexibility: Model Validation and Application

2016 ◽  
Author(s):  
Felix Güthe ◽  
Martin Gassner ◽  
Stefano Bernero ◽  
Thiemo Meeuwissen ◽  
Torsten Wind
Keyword(s):  
Gas Turbine ◽  
Experimental Studies ◽  
Operating Conditions ◽  
Theoretical Modelling ◽  
Validation Data ◽  
Part Load ◽  
Stable Conditions ◽  
Safety Margins ◽  
Wide Range ◽  
Operational Range

In recent years, market trends towards higher power generation flexibility are driving gas turbine requirements of operation at stable conditions and below environmental emission guarantees over a wide range of operating conditions, such as load, and for changing fuels. In order to achieve these targets, engine components and operation concept need to be optimized to minimise emissions (e.g. CO, NOx) and combustion instabilities, as well as to maximize component lifetime. Therefore the combination of field experience, experimental studies and theoretical modelling of flames with state of the art tools play a key role in enabling the development of such solutions. For many applications the relative changes of reactivity due to changes in operation conditions are important thus in this report a few examples are shown, where chemical kinetics simulations are used to determine the reactivity and to predict engine behaviour. The predicted trends are validated by correlating them to validation data from high pressure test rigs and real gas turbine operational data. With this approach the full operational range from highest reactivity (flashback) to lowest reactivity (blow out or CO emission increase) are covered. The study is focused on the sequential combustor (SEV) of reheat engines and addresses both the safety margins with respect to highly reactive fuels and achievable load flexibility with respect to part load CO emissions. The analysis shows that it is necessary to utilize updated kinetic mechanisms since older schemes have proved to be inaccurate. A version of the mechanism developed at NUI Galway in cooperation with Alstom and Texas A&M was used and the results are encouraging, since they are well in line with experimental test data and can be matched to GT conditions to determine, predict, and optimize their operational range. This example demonstrates nicely how a development over several years starting from fundamental basic research over experimental validation finally delivers a product for power plants. This report therefore validates the kinetic model in combination with the approach to use modelling for guidance of the GT development and extending it fuel capabilities. The GT24 / GT26 can not only be operated with H2 containing fuels, but also at very low part load conditions and with the integration of H2 from electrolysis (∼power to gas ∼PTG) the turndown capability can even be further improved. In this way the energy converted at low electricity prices can be stored and utilised at later times when it is advantageous to run the GT at lower loads increasing the overall flexibility. This development is well suited to integrate renewable energy at highly fluctuating availability and price to the energy provisioning by co-firing with conventional fuels.

scholarly journals Technological features of production of copper-based composites reinforced with cast iron granules by means of casting

2019 ◽  
pp. 114-118
Author(s):  
A. S. Kalinichenko ◽  
V. A. Sheinert ◽  
V. A. Kalinichenko ◽  
A. G. Slutsky
Keyword(s):  
Cast Iron ◽  
Composite Materials ◽  
Low Cost ◽  
Experimental Studies ◽  
Operational Reliability ◽  
Operating Conditions ◽  
High Wear Resistance ◽  
Friction Units ◽  
Wide Range ◽  
Methods Of Synthesis

Increasing the operational reliability of friction units is one of the priorities for mechanical engineering, which requires the creation of effective tribotechnical materials. First of all, this applies to sliding bearings, which are used in various friction units in a wide range of operating conditions and must meet a number of requirements: low coefficient of friction, high wear resistance and fatigue resistance, as well as good thermal conductivity, workability, corrosion resistance and machinability, low coefficient of linear expansion and low cost. It is problematic to satisfy these requirements in real conditions; therefore, different friction materials that are best suited to specific conditions have been developed. In particular, cast composite materials (LCM) have been developed, which have found application in various friction units operating in severe operating conditions. Currently, the theoretical foundations of the mechanics of reinforced composite materials are well developed, and a significant progress has been achieved in their material science. However, there are still many problems associated with the choice of optimal technology ensuring the achievement in practice of the predicted composites properties by theory, control of interfacial interaction to improve the stability of the structure and properties of CM, with the development of new types of reinforcing elements that can raise the level of composite performance.In the present work results of scientific and experimental studies on the development of casting technology (solid-liquid synthesis) for obtaining composite materials with macroheterogeneous structure have been summarized. The structures of composites are studied for different methods of synthesis, as well as for different chemical composition of cast iron granules. The prospects of using white vanadium cast iron granules as a reinforcing phase are shown.

Comparison of Deterministic and Linear Cosine Spatial Filtering of Transmission Electron Micrographs

1972 ◽  
Vol 30 ◽  
pp. 596-597
Author(s):  
David A. Ansley
Keyword(s):  
Spherical Aberration ◽  
Focal Length ◽  
Chromatic Aberration ◽  
Spatial Filter ◽  
Operating Conditions ◽  
Objective Lens ◽  
List Type ◽  
Spatial Filters ◽  
Transmission Electron ◽  
Wide Range

The coherence of the electron flux of a transmission electron microscope (TEM) limits the direct application of deconvolution techniques which have been used successfully on unmanned spacecraft programs. The theory assumes noncoherent illumination. Deconvolution of a TEM micrograph will, therefore, in general produce spurious detail rather than improved resolution.A primary goal of our research is to study the performance of several types of linear spatial filters as a function of specimen contrast, phase, and coherence. We have, therefore, developed a one-dimensional analysis and plotting program to simulate a wide 'range of operating conditions of the TEM, including adjustment of the:(1) Specimen amplitude, phase, and separation(2) Illumination wavelength, half-angle, and tilt(3) Objective lens focal length and aperture width(4) Spherical aberration, defocus, and chromatic aberration focus shift(5) Detector gamma, additive, and multiplicative noise constants(6) Type of spatial filter: linear cosine, linear sine, or deterministic

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